The present invention relates to styrene-butadiene-styrene compositions coupled with organic coupling agents carrying epoxy groups, and their use for various applications such as for example roofing, binders for road coverage or footwear compounds.
The bituminous compositions of the prior art, when used for roofing or waterproofing membranes suffer from major drawbacks; either the high temperature properties are improved at the expense of the low temperature properties, or if both ends of the temperature spectrum yield acceptable performances, the viscosity will be very; high, requiring that special equipment be used for handling the bituminous composition.
It is moreover well-known that the residue of the coupling agent remains in the copolymer formed and is thus capable of leaving toxic residues or other unwanted products in the polymers, which may be troublesome in certain uses. This phenomenon is particularly important with silicon tetrachloride (SiCl4) as coupling agent. Indeed, when SiCl4 is used as coupling agent, it is noted that lithium chloride (LiCl) is formed as by-product. The presence of LiCl is detrimental to the optical properties of copolymers and favours the thermal ageing of these copolymers.
It is known to improve the physical properties of bituminous compositions by incorporating elastomeric bock copolymers generally represented by the formula (S-B)nY wherein Y is the residue of a polyfunctional coupling agent, (S-B) represents a single arm constituted of a polydiene block B and a polyvinyl aromatic end block S. and n represents the number of arms (S-B).
The coupling agents can be selected from among polyvinyl aromatic compounds, polyepoxides, polyisocyanates, polyamines, polyaldehydes, polyhalides, polyanhydrides, polyketones, polyepoxyesters and polyesters. Combinations of different kinds of coupling agents may also be used.
Among the several polyfunctional agents of coupling available on the market, those of small residual toxicity have been preferred. For example, EP-B-344140 discloses the use of polyfunctional coupling agents of the general formula SiXnR4xe2x88x92n wherein X is a halogen, preferably Cl, R is an alkyl, cycloalkyl or aryl radical, preferably methyl, ethyl and/or phenyl and n is an integer from 2 to 4. The most frequently used coupling agent is SiCl4.
It is also known to use organic coupling agents carrying epoxy groups. Polymers of epoxidised hydrocarbons are used such as epoxidised liquid polybutadiene or epoxidised vegetable oils such as epoxidised soybean oil and epoxidised linseed oil. Each epoxy can be coupled to a chain. The number of coupling sites is undetermined and can vary according to the number of epoxy groups: it is at least 3 and preferably, it is from 4 to 6. However, the styrene-butadiene-styrene (S-B-S) compositions obtained with epoxidised triglyceride esters, sold under the name of Vikoflex, have never been used for commercial applications wherein good mechanical properties combined with low viscosity are required.
It is an object of the present invention to use organic coupling agents carrying epoxy groups in order to prepare products combining improved mechanical properties and low viscosity.
It is another object of the present invention to use organic coupling agents carring epoxy groups in order to provide improved roofing compositions.
It is a further object of the present invention to use organic coupling agents carrying epoxy groups in order to provide improved binders for road coverage applications.
It is yet a further object of the present invention to use organic coupling agents carrying epoxy groups in order to produce improved thermoplastic compounds.
The resinous thermoplastic block polymers used in the present invention are of the radially branched type with at least 3 arms. The arms of each branch are composed of substantially pure homopolymeric blocks of polymonovinylarene represented by S and polyconjugated diene represented by B.
Preferably, in the process of polymerisation used for preparing the products of the present invention, a block base copolymer is prepared by the following steps:
1) A first block of vinylaromatic monomer is polymerised to form a first block S.
2) The polymerisation is carried out at a temperature of from 20 to 60xc2x0 C., for a period of about 20 minutes, in the presence of an organolithium compound as a catalyst, and in the presence of a solvent that is an inert hydrocarbon.
3) When all the vinylaromatic monomer has been polymerised, a monomer of a conjugated diene is introduced into the solution. This monomer starts reacting entirely at the living ends of the chains to give a block copolymer of the type S-B-Li, in which B represents the conjugated diene block.
The vinylaromatic compound which constitutes the block S of the block copolymer can be styrene, vinyltoluene, vinylxylene or vinylnaphtalene or a mixture thereof.
The conjugated dienes employed ordinarily are those of 4 to 12 carbon atoms per molecule, with those of 4 to 8 carbon atoms preferred for availability. Such monomers include 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, piplerylene, 3-butyl-1,3-octadiene, 2-phenyl-1,3-butadiene, and the like. The monovinylarenes employed ordinarily contain 8 to 20, more conveniently 8 to 12 carbon atoms per molecule, including such as styrene, xcex1-methylstyrene, 1-vinyinaphtalene,2-vinyinaphtalene, as well as alkyl, cycloalkyl, aryl, alkaryl, and aralkyl derivatives thereof in which the total number of carbon atoms in the combined substituents generally is not greater than 12. Examples of sustituted monomers include 3-methylstyrene, 4-n-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 3-ethyl-4-benzylstyrene, 4-p-tolystyrene, or 4-(4-phenyl-n-butyl)styrene.
The catalyst is generally an alkyllithium, which may be branched such as those of secondary alkyl radicals, having 3 to 8 carbon atoms. However, n- and s-butyllithium are preferably used for reasons of ease of procurement and storage stability. The solvents used are generally paraffinic, cycloparaffinic and aromatic hydrocarbons and their mixtures. Examples are n-pentane, n-hexane, n-heptane, 2,2,4-trimethylpentane, cyclohexane, cyclopentane, benzene, toluene and xylene. A polar solvent, such as cyclic esters (THF) or acyclic ethers or tertiary amines, can be incorporated in order to obtain the formation of a specific polymeric microstructure, such as, for example, an increased amount of vinyl units, as well as random S/B blocks.
The peak molecular weight Mp of the base copolymer was measured by conventional Gel Permeation Chromatography (GPC) technique. The peak molecular weight Mp, so determined, varies within wide limits and is generally from 40000 to 120000 and preferably from 60000 to 80000, the polyvinylaromatic block representing from 15 to 45% by weight of the base copolymer. When this stage of the process has been reached, polymeric chains of the type S-B-Li have been formed.
The operating conditions for the GPC technique were as follows: the temperature was 23xc2x0 C., the solvant was THF and there were 5 columns in series containing ultrastyragel with pore openings ranging from 500 to 1000000 A. The solvant debit was 1 ml/min and there was a U.V. detector in series with a refraction index detector. 200 microliters of the products to be analysed, at a concentration of 0.1% in THF, were injected. The internal standard was 0.01% of tertiobutyl hydroxy toluene (THB) and the calibration was achieved using the Mark and Houwink equation in which k=1.251E-4 and xcex1=0.717. The calculations were based upon the refraction index detector and the styrene percentage was defined by the U.V. detector.
The block base copolymer terminated by a lithium atom, called the living base polymer, is then reacted with at least one coupling agent comprising at least 3 epoxy groups per mole, preferably at a rate of 0.2 to 0.75 parts per hundred parts of the total polymers obtained by coupling.
The polyfunctional treating agent is added to the polymerisation mixture under reaction conditions sufficient to form branched copolymers containing both the elastomeric and non-elatomeric blocks. Thus the polyfunctional, treating agent is added to the polymerisation mixture after the polymerisation has been essentially completed but prior to deactivation of the polymerisation initiator because it must be able of forming branched polymer by reacting with active terminal lithium atoms of the living polymer.
The styrenic content of the product is from 15 to 45 weight percent, preferably from 35 to 39 weight percent, and its peak molecular weight Mp as measured by conventional GPC technique is from 80000 to 400000, preferably from 320,000 to 380,000.
Among the coupling agents that may be used, one may cite the agents of the epoxidised vegetable oil type, the epoxidised polybutadiene or even the epoxidised tetrallylether pentaerythritol. Polyepoxidised vegetable oils such as epoxidised soybean oil or epoxidised linseed oil comprising at least 3 epoxy groups per mole, preferably 4 to 6 epoxy groups per mole will preferably be chosen. They can thus couple at least 3 chains. The number of chains coupled by the epoxy groups of the coupling agent is a function of the ratio between the amount of base polymer and the amount of coupling agent. Preferably, 5 chains are coupled.
The amounts of coupling agent to be used can easily be calculated. Indeed, the reaction between a coupling agent having a molecular weight M, and a functionality n and S-B-Li chains of molecular weight M2 carried out in a molar ratio of 1:n will theoretically give a copolymer of molecular weight M1+nM2 reduced by the molecular weight of the coupling by-product; deviations are due essentially to traces of impurities or to heat, which can, for example, deactivate the S-B-Li chains (giving copolymers with a molecular weight of about M2, as found in the final product). The total amount of coupling agent used is calculated in order to couple all the S-B-Li chains, but less can be used if preservation of an increased proportion of the S-B copolymer in the final product is desired. In the present invention, the coupling ratio is preferably from 70 to 95%. It is also noted that the amount of coupling agent may vary with the epoxy group number.
Said coupling agent is in the liquid state and is introduced in the reactor in a solvent. Preferably, said solution contains 15 weight percent of coupling agent, 15 weight percent of THF and 70 weight percent of cyclohexane. It is then heated to a temperature of from 95 to 100xc2x0 C., preferably around 97xc2x0 C., under a pressure of from 4 to 8 bars, preferably around 6 bars. The coupling reaction takes from 0.1 to 1 hour.
The block coplymer formed according to this process is radial or polybranched.
The polymer can be recovered after the polyfunctional treating agent has formed the branched block copolymers. Recovery of the polymers can be performed by conventional methods used for recovering polymer from organometal polymerisation mixtures such as treatment with materials containing active hydrogen such as alcohols or aqueous acids.
It is observed, quite surprisingly, that the viscosity of the resulting S-B-S product is significantly reduced when the coupling agent is a polyepoxide compound. The final product is therefore an ideal candidate for numerous applications. It has been utilised quite successfully for roofing membranes, binder in road applications and footwear applications.